Geoffrey Lean is Britain's longest-serving environmental correspondent, having pioneered reporting on the subject almost 40 years ago.

What caused the Deepwater Horizon disaster? There's a clue at Chernobyl

There is one huge, unanswered – maybe unanswerable – question hanging over the painstaking inquiry into the causes of BP’s Deepwater Horizon blowout, 'the Gulf of Mexico’s Chernobyl'.

Investigators have just about pieced together the physical events that led to oil and gas racing up through three and a half miles of pipework to explode on the rig, killing 11 men and leading to the release of 4.9 million barrels of oil into the Gulf of Mexico. The inquiry in Washington is also coming to the conclusion, as co-chairman William Reilly put it, that the disaster resulted from a series of decisions made by 'competent persons' which 'look like they were just plain wrong'. But nobody knows why they were made.